In recent years, use of a ferroelectric film serving as a dielectric film for a capacitor has received much attention. Such a capacitor is called a ferroelectric capacitor, and a ferroelectric memory (FeRAM: Ferro-Electric Random Access Memory) equipped with the ferroelectric capacitor is a nonvolatile memory. The ferroelectric memory has various merits such as the capability of high speed operation, low power consumption, and is excellent in write/read resistance. Further developments are expected in the future.
The ferroelectric capacitor, however, has a disadvantage in that its efficiency deteriorates easily due to hydrogen gas and moisture penetration from the outside. For example, in a ferroelectric capacitor which is composed of a bottom electrode made of a platinum (Pt) film, a ferroelectric film composed of a PbZr1-xTixO3 film (PZT film), and a top electrode made of a platinum (Pt) film being stuck in order, it has been known that when a substrate is heated at about 200° C. in the atmosphere of about 40 Pa (0.3 Torr) of a hydrogen partial pressure, the ferroelectric characteristics of the PZT film are almost lost. It is also known that, when a thermal treatment is conducted in a state that the ferroelectric capacitor absorbs moisture or in a state that moisture exists in the vicinity of the capacitor, the ferroelectricity of the ferroelectric film of the ferroelectric capacitor is remarkably reduced.
Owing to such characteristics of the existence of this property in the ferroelectric capacitor, during the manufacturing process of the ferroelectric memory, a process which incurs least moisture generation and is able to perform at temperatures as low as possible is selected as the process after formation of a ferroelectric film. In addition, as a process to deposit an interlayer insulating film, for example, a deposition process by a CVD (Chemical Vapor Deposition) method or the like using a raw material gas that generates hydrogen in a relatively small amount is selected. Furthermore, as a technology to prevent deterioration of the ferroelectric film caused by hydrogen and moisture, a technology to form an aluminum oxide film so as to cover the ferroelectric capacitor, a technology to form an aluminum oxide film on an interlayer insulating film formed on the ferroelectric capacitor, and so on have been proposed. This is because the aluminum oxide film has an ability to prevent diffusion of hydrogen and moisture. Therefore, according to these technologies, it becomes possible to prevent deterioration of the ferroelectric film caused by hydrogen and moisture by preventing hydrogen and moisture from arriving at the ferroelectric film.
These technologies are described, for example, in Patent Documents 1 to 5.
In addition, after forming the ferroelectric capacitor, aluminum (Al) wiring is formed and an oxide film is further formed as an interlayer insulating film by a plasma CVD method or the like. Even during the formation of the oxide film, deterioration of the ferroelectric capacitor sometimes occurs. Therefore, an aluminum oxide film covering the aluminum (Al) wiring is formed before formation of the oxide film.
It is difficult, however, to etch the aluminum oxide film. In order to ensure conduction of electricity between the upper layer wiring and the aluminum (Al) wiring, formation of a via hole by etching the aluminum oxide film is required, but this processing is difficult. Accordingly, the diameter of a via hole may become smaller than the designed value or a state of a tungsten plug to be formed as a via plug becomes unusual due to the influence of an etching deposition product, which sometimes causes a contact failure. As a result, a design margin becomes narrow, stable characteristics are difficult to be obtained, which lead to lowering of yield.    Patent Document 1: Japanese Patent Application Laid-open No. 2003-197878    Patent Document 2: Japanese Patent Application Laid-open No. 2001-68639    Patent Document 3: Japanese Patent Application Laid-open No. 2003-174145    Patent Document 4: Japanese Patent Application Laid-open No. 2002-176149    Patent Document 5: Japanese Patent Application Laid-open No. 2003-100994    Patent Document 6: Japanese Patent Application Laid-open No. Sho 60-262443    Patent Document 7: Japanese Patent Application Laid-open No. Sho 63-117429    Patent Document 8: Japanese Patent Application Laid-open No. Hei 10-256254